1. Field of the Invention
This invention generally relates to a method of delivering doses of a gaseous drug through an ambulatory device to treat a patient with lung disease. The invention more particularly relates to an ambulatory device that provides a specific dose of a gaseous drug to a patient on each breath and can vary that dose to adjust to the patient's needs, as well as deliver it at various flow rates to maximize comfort and decrease noise.
2. Description of Related Art
The treatment of patients with lung disease often involves the use of ambulatory oxygen dosing systems.
Oxygen dosing systems are currently commonly referred to as conserving devices because they only allow oxygen to be provided at fixed flows during a specific portion of the inhalation cycle. Conservers typically get oxygen from high pressure tanks that are delivered to the patient by an oxygen dealer. The design of these units is to conserve oxygen so that oxygen is not provided when the patient cannot use it and therefore it is not wasted. These types of devices were focused on using less oxygen so that deliveries of the tanks to the patient were less frequent and thereby saving costs. However, while these conservers are often effective at using less oxygen, they do not dose the patient properly. Clinical information on these types of devices can be found in, “A Guide to Understanding Oxygen Conserving Devices 2003” by Valley Inspired Products which is herein incorporated by reference.
Research on oxygen conserving devices dosing can be found in the following documents which are herein incorporated by reference: (a) Trina M. Limberg, Roberta S. Colvin, Maria Correa, Rosanna Costello, Cindy G. Morgan, and Andrew L. Reis, “Changes in Supplemental Oxygen Prescription in Pulmonary Rehabilitation”; (b) A. Somfay, J. Porszasz, S. M. Lee, and R. Casaburi, “Dose-Response Effect of Oxygen on Hyperinflation and Exercise Endurance in Nonhypoxaemic COPD Patients”, European Respiratory Journal, July 2001, volume 18 at 77-84; (c) Luis Puente-Maestu, Julia Garcia de Pedro, Yolanda Marinez-Abad, Jose Maria Ruiz de Ona, Daniel Llorente, and Jose Manuel Cubillo, “Dyspnea, Ventilatory Pattern and Changes in Dynamic Hyperinflation Related to the Intensity of Constant Work Rate Exercise in COPD”, Chest, August 2005, volume 128 at 651-656; (d) O. Diaz, C. Villafranca, H. Ghezzo, G. Borzone, A. Leiva, J. Milic-Emili, and C. Lisboa, “Breathing Pattern and Gas Exchange at Peak Exercise in COPD Patients With and Without Tidal Flow Limitation at Rest”, European Respiratory Journal, June 2001, volume 17 at 1120-1127; and (e) Peters, MM, Webb, K A, and O'donnell, De, “Combined Physiological Effects of Bronchodilators and Hyperoxia on Exertional Dyspnea in Normoxic COPD”, Thorax, July 2006, volume 61 at 559-567.
The fixed flow conserver devices can be categorized into either constant minute volume or constant volume conservers.
Constant volume devices really are fixed flow/variable time. On a device that has patient settings of 1-6, which can correspond to a patient's LPM prescription, each setting would provide a fixed volume per breath delivered. An example of this type of device can be seen in U.S. Pat. Nos. 5,005,570 and 5,370,112 to Perkins. These types of devices in commercial application typically have different settings to provide different volumes of oxygen. These devices typically provide for 16 cc of volume for each setting, so that a patient who is on a 2 setting would receive 32 cc of oxygen at each inhalation cycle. The flow is fixed by an orifice against a known pressure and the device calculates the valve on-time to deliver a desired volume. This flow and valve on-time is the same for a patient who is breathing at 12 breaths per minute (“BPM”) as it is for a patient who is breathing at 35 BPM. The device is designed to handle the highest expected breath rate and therefore, delivers a higher than necessary flow in a shorter than necessary window for patients breathing at a more relaxed rate.
Constant minute volume devices simply act as on/off valves at a fixed flow and do not predetermine a dose, but rather are demand valves. They turn on during inhalation, and turn off during exhalation. These devices simply supply the patients' prescription flow. Since the I:E ratio is thought to remain constant, 1:2 for example, it is thought that the valve will be on for a fixed percentage of the time in the course of a minute, and therefore are called constant minute devices. Constant minute volumes also often insert an accumulator chamber that is replenished during valve off times. Assuming that the device fills this accumulator at a fixed rate (often 0.7-1 SLPM), then the patient depletes this on every breath. The patient can never get more than the limit of 1 SLPM of oxygen and if they breathe too fast, the accumulator can not be filled due to recovery time.
The above non-feedback devices do not adjust for a larger dose per breath as the patient ambulates, and in many cases, the patients will desaturate, i.e. have low oxygen levels in bloodstream.
Also, because the non-adjusting units give fixed doses at fixed flows, they do not adjust the flow down to minimize the flow required for that breath dose of oxygen. Fixed volume units give a specific, repeated dose by opening the valve for a fixed time, regardless of the inhalation time. Because the flow is not minimized there is noise created through the nasal canula, creating an unpleasant experience for the oxygen patient because the flow can startle the patient and cause nasal dryness.
The above prior art devices also are inefficient because oxygen is wasted. Oxygen from the above devices can be delivered during the second half of inhalation. Oxygen delivered during the second half of inhalation fills the upper airway where no gas exchange takes place and has no therapeutic value. Additionally the above devices do not deliver doses that fit the patient's need when their breath rate rises.
Further, some clinical personnel have migrated to using two prescriptions for a patient; one for rest and another, higher setting for the patient to use during ambulation. This points out the need for additional oxygen during exercise, but also puts the burden on the patient to remember to turn up their conserver when they get up and start walking, and then to remember to turn it back down when they sit down. Many of these patients are in their later years and can often forget to turn the device up or down, resulting in desaturation, or oxygen being wasted respectively.
Other than the above devices there are devices that use pulse oximetry as a feedback method and then adjusts to provide a target oxygen saturation. Examples of such devices can be found in U.S. Pat. No. 6,532,958 to Buan et al.; U.S. Patent Application Publication No. 20060225737 to Iobbi; U.S. Patent Application Publication No. 20060213519 to Schmidt; U.S. Patent Application Publication No. 20060011199 to Abdul-Aziz; U.S. Patent Application Publication No. 20060005842 to Abdul-Aziz; U.S. Patent Application Publication No. 20040159323 to Schmidt; and U.S. Patent Application Publication No. 20030145852 to Schmidt.
However, oximetry is a very cumbersome means of feedback. A separate oximetry sensor must be attached to the patient usually on the patient's finger. Additionally, oximetry is not very accurate on a patient who is ambulatory.
U.S. Pat. No. 6,880,556 tries to address the deficiencies with the prior art conservers. To do this U.S. Pat. No. 6,880,556 uses a predetermined normal breath rate. This breath rate is used for all patients. A person of ordinary skill in the art would believe that there is a universal breath rate that could be used, such as 20 bpm, that is the normal resting breath rate for all people and that this could be used to effectively dose all patients. U.S. Pat. No. 6,880,556 uses an on/off valve to deliver a volume of oxygen. All of the oxygen is delivered at the same flow rate.
Historically, everybody skilled in the art and in the industry assume that the normal resting breath rate is 20 breaths per minute. One of ordinary skill in the art would expect to be able to use 20 breaths per minute; and that at 20 breaths per minute, all patients would be kept saturated.
However, through extensive research and clinical work we have figured out that there is not a normal resting breath rate that applies to all people. We have discovered that normal resting breath rate is not the same for every patient. There is a normal resting breath rate for each and every patient that is particular to that patient and the normal resting breath rate for each individual patient varies over time. It can even vary through the day. The normal resting breath rate for a person can vary from hour to hour.